Problem: $-9uv + v - 5w - 4 = 9v + 8w - 9$ Solve for $u$.
Solution: Combine constant terms on the right. $-9uv + v - 5w - {4} = 9v + 8w - {9}$ $-9uv + v - 5w = 9v + 8w - {5}$ Combine $w$ terms on the right. $-9uv + v - {5w} = 9v + {8w} - 5$ $-9uv + v = 9v + {13w} - 5$ Combine $v$ terms on the right. $-9uv + {v} = {9v} + 13w - 5$ $-9uv = {8v} + 13w - 5$ Isolate $u$ $-{9}u{v} = 8v + 13w - 5$ $u = \dfrac{ 8v + 13w - 5 }{ -{9v} }$ Swap the signs so the denominator isn't negative. $u = \dfrac{ -{8}v - {13}w + {5} }{ {9v} }$